Work as a buyer and depending on the food item it can range from 8-16wks stock cover.

A few reasons.

Stability of supply and to negate potential risk of loss of supply. Food is important and people go crazy when theres no food on shelves.

Minnium order quantities are a factor when being ordered from a supplier so it makes commercial sense.

Waste isn't a massive factor for a lot of cupbard foods as theyll have long shelf life anyway and when it comes to Fresh stockholding isn't a thing.

You will have some niche food areas like wines and spirits that arent really effected by code life they can be held for certain times of year like new years etc.